Which row is correct about the structure of proteins?
- APrimary structure is the number of amino acids present in a protein; secondary structure is the left-handed spiral formed by the primary structure; quaternary structure is the sub-unit polypeptides that link together to form a protein.
- BPrimary structure is the order of amino acids present in a protein encoded by DNA; secondary structure is the coiling of a chain of amino acids to form a $\beta$-pleated sheet or $\alpha$-helix; quaternary structure contains two types of polypeptide that interact forming the shape of a protein.
- CPrimary structure is the result of translation of an mRNA molecule by a ribosome into a chain of amino acids; secondary structure occurs because of attraction between hydrogen and oxygen atoms in the peptide bonds; quaternary structure is formed by four polypeptides and an additional reactive group attached to the protein.
- DPrimary structure is the sequence of amino acids in a protein coded by an mRNA molecule; secondary structure is formed by hydrogen bonding between amino acids forming the primary structure; quaternary structure is formed by the linking together of more than one polypeptide to form a protein.